Make It Work Or Start Over?

I'm going to be working on an alarm system site that has been redesigned several times over the past 10 years it has been around. It has a page rank of 3/10, but does not have any SEO to speak of at all. It does not rank for any keywords that I can find.
The company is being taken over by someone who has a good understanding of the importance of a web presence, and wants to do things the correct way form here on out.
The domain name does not have any keywords in it. There are no relevant backlinks that I can find, But it still comes up as a pagerank 3/10, and I'm guess that it is because of the age of the domain (over 10 years).
My question is, which is the better plan...
Create a new site, on a new domain using a keyword in the domain (and direct the old domain name to the new domain)